1. Field of the Invention
This invention relates to a label for in-mold decorating, which is inserted into a mold in contact with the cavity wall to manufacture labeled containers. Preferable molding methods for in-mold decorating include blow molding of a thermoplastic resin hot parison, injection molding of a molten thermoplastic resin, and vacuum forming or pressure forming of a heat-softened thermoplastic resin sheet. The present invention also relates to a labeled resin molded article.
2. Discussion of the Background
In-mold decorating for producing a labeled container is carried out by inserting a label into a mold and molding a resin in the mold and forming into a container by injection molding, blow molding, differential pressure forming, foaming, and the like (see, e.g., JP-A-58-69015 and EP 254923). Known labels for use in in-mold decorating include gravure-printed resin films, multicolor offset-printed synthetic paper (see, e.g., JP-B-2-7814 and JP-A-2-84319), and aluminum labels composed of aluminum foil laminated with a high pressure processed low density polyethylene or an ethylene-vinyl acetate copolymer and having the aluminum foil gravure-printed.
When carrying out in-mold decorating with an automatic label feeder to feed a label to a prescribed position on the inner wall of a mold, if the labels do not have sufficient antistatic properties or if a stack of labels is not destaticized, particularly in a low humidity environment or in winter, the undesirable result is that two or more labels may be erroneously fed at one time, or a label is not fed to the right position, or a label falls uselessly.
Labels having insufficient antistatic properties are also accompanied by feeding difficulties in printing, particularly offset printing, which requires frequently suspending and resuming of the printing machine.
In order to eliminate the above-mentioned inconveniences, the following solutions have been proposed: (1) labels for in-mold decorating having a migrating low-molecular antistatic agent, such as sorbitan monooleate or glycerol monostearate, incorporated into the heat-sealable resin layer thereof typically comprising a polyethylene resin; and (2) labels for in-mold decorating having on the heat-sealable polyethylene resin layer thereof an antistatic coat of a low-molecular antistatic agent, such as a polyoxyethylene derivative, applied and dried.
The antistatic properties of both the proposed labels (1) and (2) have only a short duration, however. In addition, the labels (1) have the disadvantage that the antistatic agent in the heat-sealable resin layer migrates to the surface and thus considerably impairs the fusion bonding properties, resulting in generation of rejects, such as non-labeled containers and labeled containers of which the label has blisters.
To solve the problems it has been proposed to incorporate into a heat-sealable resin a polyether ester amide, which is a non-tacky, long-lasting antistatic agent (see JP-A-11-352888). The polyether ester amide, however, when incorporated into a heat-sealable resin and extruded through a T-die into a film, accumulates near the outlet of the T-die and deteriorates to form a considerable amount of so-called resin-like stain, or it accumulates dirt on the rolls in the production line that are in contact with the heat-sealable resin layer. Since such stains and dirt can cause film defects, the production line must be suspended frequently to clean the die or the rolls.
Accordingly, there is a great need for a label for in-mold decorating that avoids the above-mentioned problems.
Accordingly, one object of the present invention is to provide a label for in-mold decorating, which does not produce the above-mentioned resin-like stain.
Another object of the present invention is to provide a label for in-mold decorating which, does not contaminate the rolls in a label production line.
Another object of the present invention is to provide a label for in-mold decorating, which is free from inconveniences caused by insufficient antistatic properties in printing, cutting, blanking, and inserting into a mold irrespective of the working environment.
Another object of the present invention is to provide a label for in-mold decorating, which exhibits high adhesive strength.
Another object of the present invention is to provide a label for in-mold decorating, which exhibits high adhesive strength to containers.
These and other objects have now been attained by the present invention, the first embodiment of which provides a label for in-mold decorating, which includes:
(I) a thermoplastic resin film base layer;
(II) an interlayer overlying the base layer and including:
(a) a thermoplastic resin composition, and
(b) at least one antistatic agent; and
(III) a heat-sealable resin layer overlying the interlayer.
Another embodiment of the invention provides a labeled, resin molded article, which includes the above-mentioned label integrally adhered thereto by thermal fusion bonding.
Another embodiment of the invention provides a labeled, resin molded article, which includes the above-mentioned label.
Another embodiment of the invention provides a method for labeling, which includes placing the above-mentioned label into a mold, placing a moldable resin in the mold in contact with the label, and molding or forming the moldable resin into an article that includes the label.